The 15-year study looked at prescribing data for all 310,000 adults resident in the Tayside region between 1995 and 2010.

As well as the soaring rates of drug prescriptions, it found that elderly people, especially those living in care homes or more deprived areas, were more likely to be prescribed more than 10 drugs.

Prof Bruce Guthrie, who led the project, said potentially serious clashes between drugs prescribed for different conditions was "common".

'Considerable harm'

He said: "Prescribed drugs significantly improve a range of health outcomes, but they can also cause considerable harm - approximately 6.5% of all emergency hospital admissions are attributable to adverse drug events and at least half of these are judged preventable.

"Our study shows there has been a significant rise in the numbers of people receiving multiple drugs.

"This raises concerns because the simultaneous use of large numbers of drugs, what we call polypharmacy, can cause serious harm in some patients."

In 1995, one in 17 adults in the Tayside area were prescribed drugs with potentially serious interactions.

By 2010, that number had more than doubled to one in eight - with 44% of people aged 70 or older prescribed drugs which could have serious interactions.

Prof Guthrie said: "Drug regimens are increasingly complex and potentially harmful. More research is needed to better understand the impact on people's health of multiple interacting drugs."